Leukotriene (LT) C4 synthase (LTC4S) is the pivotal enzyme in the biosynthesis of LTC4, the parent compound of the cysteinyl leukotrienes (cysLTs). These lipid mediators have profound biologic effects and contribute to the pathobiology of bronchial asthma and other inflammatory diseases acting through the cysteinyl leukotriene 1 receptor (CysLT1R) and CysLT2R. Interleukin (IL) 4, a Th2 cytokine that is implicated in bronchial asthma, upregulates LTC4S in human and mouse mast cells (MCs) and enhances their ability to generate cysLTs. The objectives of this project are to define the signal transduction pathway involved in the upregulation of LTC4S in mouse MCs by IL-4 (Specific Aim 1) and to define the role of cysLTs and their receptors in the pathobiology of pulmonary inflammation (Specific Aim 2). To assess the signal transduction pathway involved in the upregulation of LTC4S by IL-4, we will examine the effect of IL-4 on LTC4S activity in vitro and in vivo using signal transducer activator of transcription (STAT) 6 and phosphoinositide 3 kinase (PI3K) pathway-defective mice and their wild type controls. We will examine the binding of STAT6 to the consensus STAT6 motif of the LTC4S gene in bone marrow derived MCs by electrophoretic mobility shift assay and by chromatin immunoprecipitation with anti-STAT6 antibody followed by PCR of the precipitated genomic DNA. To analyze the role of the cysLTs in acute and chronic aerosol antigen induced pulmonary inflammation, the generation of a mouse strain with targeted disruption of CysLT2R is planned so as to allow comparison with the CysLT1R null strain. Parallel studies will be conducted with mice that are null for LTC4S (cysLT deficient), with mice that overexpress the human LTC4S (cysLT overproduction), and with mice deficient in each of the CysLTRs, CysLT1R and CysLT2R (selective absence of the target tissue response to cysLTs), to clarify the role of the cysLTs in the acute responses of altered permeability and cellular influx and in chronic responses of mucus gland hyperplasia, smooth muscle hyperplasia, and basement membrane thickening.